The development of offshore gas or gas condensate fields of smaller size has often been considered as unprofitable because the costs of bringing the product therefrom onto the market would have been too high. Using technologies known thus far often requires complicated preprocessing and production plants for the preparation of products which are more suitable for the transport away from an exploitation field than an unprocessed well stream. In particular it has been common practice to separate liquids and solid particles, and any heavier hydrocarbons, from the well stream and then to process further constituents of the well stream individually, such as the extracted gas.
An example of the prior art is described in U.S. Pat. Nos. 6,003,603 and 5,878,814, which relates to a method and system for offshore production of liquefied natural gas (LNG), wherein the well stream is supplied from a subsea production plant to a pipeline, in which it is cooled by the surrounding sea water. Then the well stream is supplied to a conversion plant provided on a ship, wherein liquids and solid particles are extracted and at least a part of the remaining gas is converted to liquid form for the transfer to storage tanks on board the ship.
Another example of the prior art is described in U.S. Pat. No. 6,378,330 which relates to a process for making pressurized liquefied natural gas (PLNG) from a gas stream rich in methane, wherein gas is condensed by first being cooled and then expanded. If the stream of natural gas contains heavier hydrocarbons which may freeze out during the liquefaction, they must, however, be removed prior thereto.
Furthermore, U.S. Pat. No. 5,199,266 describes a method of dealing with petroleum gas from an oil or gas production field comprising ethane and heavier hydrocarbons, wherein liquids and solids are separated from a well stream and the gas of the well stream is dried, cooled and possibly processed further prior to condensation and the placement of condensed gas in storage tanks. In U.S. Pat. No. 6,094,937 describes a method of liquefaction and/or conditioning of a compressed gas/condensate from a petroleum deposit especially a compressed gas/condensate flow which has been separated from a crude oil extracted from an offshore oil field.
Using the technologies known thus far and disclosed in the above publications, the feed is in each case subjected to a preprocessing prior to the condensation process itself. In particular it is presupposed that liquids and solids, and any heavier hydrocarbons, are separated in advance. The known techniques referred to all focus on making liquefied natural gas of some quality or other, that may be brought ashore from a location at sea. None of the publications is seen to be concerned with the other constituents of the well stream. According to U.S. Pat. Nos. 6,003,603 and 5,878,814, for example, the extracted liquids and solids are transferred to a container with no indication as to what is done with the contents of the container when it is full.
Therefore, in such offshore production of liquefied natural gas, there may be a problem in respect of such components that traditionally are extracted, such as oily sands and water, which must be transported away, or otherwise be deposited in situ. Common to the approaches disclosed in the publications above is that they also require costly processing plants, sometimes drier/dehydration and regenerator/cleaning systems, too.
Thus, there is a need for a technological solution, by means of which smaller gas or gas condensate fields can be developed in a more cost efficient manner than by the technologies known so far.